This invention relates to a hydrodynamic brake.
Known brakes of this type generally have a rotor blade wheel and a stator blade wheel which together form a toroidal work chamber; each of the two blade wheels having a series of substantially flat blades which are stationary relative to their respective blade wheel and--in order to increase the braking action--are inclined relative to the axis of rotation of the rotor blade wheel; and various devices also being known for controlling the braking action of the brake.
For example, in known hydrodynamic brakes of this type, the brake torque may be controlled by varying the degree of filling of the work chamber by the braking fluid; see, for example, German Pat. No. 28 55 654-U.S. Pat. No. 4,276,970. This and all other prior art materials mentioned herein are expressly incorporated by reference. For this purpose, the known brake is provided with control valves outside the torus-shaped work chamber, in the feed and/or discharge lines for the working liquid, said valves determining how much the work chamber is filled.
Brakes of this type have proven themselves effective, particularly as vehicle brakes. They have, among other things, the advantage that the two blade wheels have a simple shape, since each blade is stationary relative to its respective blade wheel, i.e. the blades are rigidly connected to the two wheel bodies. The cross-sectional profile of the torus-shaped work chamber is, at least approximately, of circular shape. In order to achieve the greatest possible braking action with such brakes, with a predetermined outside diameter, the blades of both blade wheels are always inclined with respect to the axial direction.
Difficulties occur, however, when such a hydrodynamic brake is to serve in a stationary power transmission unit for the sensitive braking of one of the gear members of a differential; see PCT patent application WO 86/02983--U.S. Pat. No. 4,726,255. That publication discloses that several types of such a power transmission unit are known: some types have a hydrodynamic input coupling; in another type the hydrodynamic input coupling is lacking, in which connection the driven speed of rotation of the power transmission unit can be varied by changing the brake torque of the hydrodynamic brake. In accordance with said publication, the changing of the brake torque is effected by changing the degree of filling of the hydrodynamic brake. One disadvantage of this method is that it is relatively difficult to stably maintain a given desired driven speed of rotation of the power transmission unit, or to change from a previous driven speed of rotation to another driven speed of rotation.